Hydrophone arrays are widely used in acoustic detection systems. In such systems signals received from discrete sensors are processed for signal detection and for acquiring information on the angle of incidence. Signal processing requirements of sonar arrays are often quite severe and in some cases real time processing cannot be acomplished even with large computers. Furthermore, a large amplitude signal from one source tends to obscure a small signal from another source due to the limited dynamic range of individual hydrophones.
Optical fiber acoustic sensors recently introduced into the art employ single mode optical fibers arranged in the form of a Mach-Zender interferometer provided with parallel optical paths for defining sensing and reference arms. In this type of sensor, the acoustic wave changes the optical path length of the sensing arm fiber relative to the path length of the reference arm fiber. An example of this type of acoustic sensor is disclosed and claimed in U.S. Pat. No. 4,162,397 issued July 24, 1979 to Joseph A. Bucaro et al., for Fiber Optic Sensor. Further insight into acoustic sensors of this type are illustrated and discussed in Applied Optics 16, 1761 (77).
An acoustic sensor according to the Mach-Zender arrangement has only one of its fibers exposed to the environment in which it operates. The pressure of environmental fluctuations, such as temperature changes or interfering sound waves, cause a phase shift in light passing through the separate arms.